This invention relates to a device for controlling the feed of at least one yarn to a textile machine and for compensating any pulling and excess tension exerted on said yarn during said feed, the yarn being unwound from a usual bobbin.
Each yarn fed to a textile machine must be monitored for breakage during its unwinding from the corresponding bobbin so that if breakage occurs the machine is halted in order not to produce defective articles. There is also the problem of compensating any excess tension arising in the yarn during its feed to the textile machine, in order to avoid such breakage.
Various anti-pull devices are known, such as those described in U.S. Pat. Nos. 3,789,631 and 3,863,466. These devices are able to act if the yarn is subjected to pulling or excess tension, in order to release it by dropping or disengaging an arm opposed by a force-adjustable spring, the movement of said arm, on releasing the yarn, causing stoppage of the textile machine to which the device is applied.
Such anti-pull devices hence prevent breakage of the yarn under control, so reducing production defects or damage to the textile machine.
These anti-pull devices are generally located above the textile machine at a height difficult to reach by the operator, and when the yarn falls on its release by the movable arm this arm has to be returned to its working position (i.e. the device has to be reset) and the corresponding yarn has to be returned to it (either while it is being moved or afterwards). This has to be done either manually by the operator or by complicated and costly mechanisms, such as that described in U.S. Pat. No. 3,863,466. In either case the cost of this operation negatively affects the cost of the finished product.
In addition, to prevent an excessive number of stoppages of the textile machine the springs associated with the movable arm (or release arm) of these devices are adjusted such that the arm is able to release the yarn only if very strong pulling or excess tension occurs. In many textile machine operations, such as in stocking production, this can cause small holes or streaking in the knitwork, leading to defective article production.
In addition, these devices cannot compensate excess tension because they react drastically on the textile machine operation in the sense that they merely halt it whether the yarn is subjected to small or large excess tension.